1. Field of the Invention
The present invention relates to a cylindrical fluid-filled vibration-damping device used as vehicle engine mounts or the like.
2. Description of the Related Art
A known cylindrical fluid-filled vibration-damping device of this kind includes: an inner cylindrical metal sleeve, and a tubular intermediate metal sleeve as well as an outer cylindrical metal sleeve that are disposed about the inner cylindrical metal sleeve with a radial spacing therebetween. A stopper member is mounted on the outer circumferential surface of the inner sleeve, protruding radially in one direction towards an opening in the intermediate sleeve, with its tip or distal end opposed to the inner circumferential surface of the outer cylindrical sleeve with a gap therebetween. A rubber elastic body is disposed in between and elastically connects the inner cylindrical sleeve and the intermediate sleeve. The rubber elastic body is formed with a recessed portion opening towards the outer cylindrical sleeve and surrounding the stopper member, and a diaphragm portion radially opposite to the recessed portion. This cylindrical fluid-filled vibration-damping device includes a primary fluid chamber that formed between the recessed portion and the outer sleeve, and an auxiliary fluid chamber formed between the diaphragm portion and the outer cylindrical sleeve. An orifice passage is formed between the outer and the intermediate sleeve for connecting the primary and auxiliary fluid chambers to each other to permit a fluid communication between the chambers.
This vibration-damping device is installed on a vehicle by fixing the inner cylindrical sleeve and the outer cylindrical sleeve on the engine side member and the vehicle body side member with the primary fluid chamber and auxiliary fluid chamber disposed vertically. Upon vibrational input between the inner and outer cylindrical sleeves due to the vibration of the engine or the like, the vibration-damping device is able to damp those vibrations with the elastic action of the rubber elastic body and the resonance action of the fluid column of fluid flowing through the orifice passage between the primary fluid chamber and auxiliary fluid chamber. When vibrational input in a so-called “bound” direction becomes excessive, the stopper member strikes the inner circumferential surface of the opposing outer cylinder sleeve, whereby excessive relative displacement between the inner and outer cylindrical sleeves is suppressed and vibration is rapidly damped. However, the aforementioned stopper member is formed of a hard material such as metal or resin and, furthermore, its surface is covered with a thin rubber coating layer. At the time of the above mentioned excessive vibrational input, stick slip occurs easily because of the tip side firmly striking and grinding against the metal surface of the outer cylindrical sleeve. A problem is that noise generated along with this stick slip causes discomfort to passengers in the vehicle.
With this regards, JP-A-2002-323085, for example, discloses the use of a cylindrical rubber mount with a stopper disposed projecting towards an outer cylindrical sleeve from an inner axial sleeve, and the connection of the inner axial sleeve with the outer cylindrical sleeve by a main rubber elastic body. In this cylindrical rubber mount, the stopper is formed of a hard stopper body and a shock absorbing rubber layer adhered to the projecting tip surface thereof. Furthermore, the striking surface of the outer cylindrical sleeve which is struck by the stopper is a surface to which no adhesive is adhered. As a result, stick slip is prevented from occurring when the stopper strikes the striking surface of the outer cylindrical sleeve. Also, as disclosed in JP-U-7-3073, for example, another vibration-damping device is known wherein surface variations are formed on either a stopper comprising a rubber elastic body or the inner circumferential surface of the outer cylindrical sleeve which is struck by the stopper. The coefficient of friction of the striking surface is reduced, whereby stick slip that may occur when the stopper strikes is suppressed.
However, the aforementioned cylindrical fluid-filled vibration-damping devices are not necessarily sufficient to suppress stick slip because of the magnitude of the principal vibrational input and it is necessary to further suppress noise within the vehicle in order to improve the ride quality of the vehicle. It is therefore desirable to further ensure the suppression of stick slip of the stopper for the fluid-filled cylindrical vibration-damping devices.